Method of firing continously operating kilns for ceramic products



Dec. 30, 1969 A. HASSLER 3,487,135

METHOD OF FIRING CONTINUOUSLY OPERATING KILNS FOR CERAMIC PRODUCTS FiledFeb. 25, 1966 Sheets-Sheet 1 IN V EN TOR.

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HTTORNEVS Dec. 30, 1969 A. HASSLER 3,487,135 METHOD OF FIRINGCONTINUOUSLY OPERATING KILNS FOR CERAMIC "PRODUCTS Filed Feb. 25, 1966 2Sheets-Sheet 2 3 1\ s Q h Lk {I i i I no I 4 I N l l l t N l l I '0 INVEN TOR.

Hnareas Haas/e United States Patent 3 487,135 METHOD OF FIRINGCONTINOUSLY OPERATING KILNS FOR CERAMIC PRODUCTS Andreas Hassler,Jahnstrasse 45, 7904 Erbach/Wurttemberg, Germany Filed Feb. 25, 1966,Ser. No. 530,192 Claims priority, application Germany, Mar. 1, 1965, H55,338; Nov. 25, 1965, H 57,838 Int. Cl. C04b 33/32, 35/64; M71: 9/10;F27d 19/00 US. Cl. 264-56 6 Claims ABSTRACT OF THE DISCLOSURE A methodof firing continuously operating kilns for ceramics and like productsincluding the step of causing the firing gas to flow alternately withand against the movement of material being fired. The alternate flow ispreferably rhythmic and adjustable.

The operation of continuous kilns, for example tunnel kilns, for ceramicproducts, as counterfiow heat exchanges, wherein a stream of air or gasis moved in the opposite direction to the direction of travel of thematerial to be fired, and finally exhausted as flue gas adjacent theinlet to the kiln, is known. Fuel is fed to the kiln, for example bymeans of a lateral heater or of a ceilin heater, in the main firingzone, substantially in the middle of the kiln. The fuel fed into htefiring zone gives its heat at each burner or row of burners to the airin the combustion chamber, which until it reaches the next burner or rowof burners gives olf heat to the material to be fired. [During this timethe firing air drops in temperatures so that at the next burner or rowof burners it is heated up. A constant reheating of the firing airrepeatedly occurs in the spaces between the heaters in the length of thekiln. I

As the kiln uses, on the one hand, a given amount of fuel and, as on theother hand, a given amount of air passes through the kiln, exceptionalheat exchange relationships result herefrom. The amount of air passingthrough the kiln over a unit of time, is in the main determined, becauseof the counter flow heat exchange method, by the amount of material tobe fired passing through per unit of time. As large differences oftemperature are undesirable for the firing of ceramics, inadmissa blylarge falls in temperature are produced from one burner or row ofburners to the other in the counter flow method with intermediateheating up of the firing air. Drops in temperature of from 50100 C. arenot uncommon. Consequently the employment of continuous longitudinal andtransverse circulation of air in the heating up and cooling down zonesof such kilns, has already been adopted in order to improve the heattransfer relationships between air or firing air on the one hand and onthe material to be fired on the other. Hitherto, success has not beenachieved in obtaining an improvement in the heat transfer relationshipsdue to the high temperatures in the firing zones of such kilns.

In contrast to this, a method is provided according to the invention,which, in a simple manner, makes it possible considerably to improve theheat exchange in a continuous kiln so that higher throughput and qualitycan be achieved.

The invention will now be described further by way of example withreference to the accompanying drawings.

FIG. 1 illustrates the known counter flow method in a tunnel kiln, theflue gas being exhausted at the entry to the kiln by a chimney 1.

The firing air is moved in the opposite direction to that of thematerial to be fired placed on the trolley 2.

In the mehod according to the invention illustrated in FIG. 2, incontrast thereto, the direction of the air flow in the kiln isperiodically reversed so that the chamber of the kiln is operated atshort intervals of the time with the air flowing alternately in theopposite and in the same direction as the material to be fired ismoving. The duration of the flow in each direction may be selected as issuitable and if desired, may be different in each direction. Further,the air pressures in each direction may be selected at will inaccordance with requirements. For carrying out the method devices knownper se can be used, for example, a fan 3 at the inlet to the kiln and afurther fan 4 at the outlet from the kiln. A connection pipe 5 may alsobe provided. Instead of the fan 3, a fan located in the flue gas chimney1 may be used.

The firing method according to the invention may be partially used alsoin firing kilns forceramics which are operated in the continuous orreversing principle, as shown in FIGS. 3 and 4.

The reference numbers 1, 2 and 5 indicate in FIGS. 3 and 4 thecorresponding parts similarly marked in FIGS. 1 and 2. Only the fans 6to 10 which replace to the fans 3 and 4 in FIG. 2 have been remarked dueto the altered arrangement of the flow circuits.

The method can be used for example only in the heating up, cooling, orfiring zone. A use is furthermore also possible in such a way that, inthe reversing method according to the invention, in each case only twozones are inclnded.

The method may also be used in such a way that the individual reversedflows overlap (FIG. 4). According to the prior art, the heating up andthe cooling, especially the latter, of ceramic products presentconsiderable difficulties which are only met in an imperfect manner bythe known counter-flow firing method with which tunnel kilns for exampleare frequently operated. The new reversing flow firing method makes itpossible, for example in the cooling process, to move a considerablylarger amount of air in alternating directions, and indeed, does notdamage the throughput of air through the cooling zone. Thereby very goodheat transfer relationships are provided for an even cooling or heatingup.

Ifseveral kilns are available or could conveniently be included, it isadvantageous that the rhythmic reversible flow circuit through one kilnis returned through at least a second kiln. By this separate returnpipes 5 are saved.

I claim:

1. A method of firing continuously operating kilns for ceramic productscomprising the steps of causing a firing gas to flow through at leastpart of the kiln opposite to the direction of passage through the kilnof the material to be fired, and superposing on said flow a rhythmicallylengthwise oscillating gas flow alternately opposite to and in the samedirection as the direction of passage through the kiln of the materialto be fired.

2. A method as set forth in claim 1 in which the respective durations offlow in the two directions are adjustable.

3. A method as set forth in claim 1 in which the gas pressure during theflow in the one direction is different from the gas pressure during theflow in the other direction.

4. A method vas set forth in claim 1 in which the said alterante flow iscaused to occur over one longitudinal part of the kiln only,

5. A method as set forth in claim 1 in which alternate flow is caused tooccur independently over more than one longitudinal part of the kiln.

6. A method as set forth in claim 1 in which said alternate flow iscaused to occur over those zones of the kiln where the material to befired is first heated and secondly fired.

References Cited UNITED STATES PATENTS US. Cl. X.R.

